1. Field of the Invention
The present invention relates to a rotation sensor such as a throttle position sensor, attached to a throttle valve, for detecting an opening level of the valve, and more particularly to a rotation sensor accommodable to the eccentricity of a rotation portion of the valve relative to the rotating shaft of the sensor.
2. Description of the Related Art
FIG. 23 is a schematic diagram showing a conventional rotation sensor as described above. As shown in the figure, a shaft 52 is coupled to a rotor 51 of a detection side, the shaft 52 is rotatably supported at a location of a bearing 53, and a magnetized code plate 54 that is integrally connected to the tip of the shaft 52. In the vicinity of the circumference of the code plate 54 that is disposed a magnetism detecting element 55, which is supported by a casing (not shown).
By way of example, the conventional rotation sensor, which has a so-called one-point support configuration in which the shaft 52 is supported at one point, has the shaft 52 supported by the bearing 53 with some backlash so that it is freely rotatable. If the rotor 51 is attached to the shaft 52 with their center axes in misalignment or if in its place the rotor 51 itself rotates eccentrically, then the code plate 54 will rotate eccentrically, and a gap G between the code plate and the magnetism detecting element 55 will change greatly. As a consequence, a linear output will not be obtained in a magnetic variable resistor. This has been a disadvantage of conventional rotation sensors.
If the shaft 52 is supported at two points to solve this disadvantage, although a relative positional relationship between the code plate 54 and the magnetism detecting element 55 can be maintained to a degree of the clearance between the shaft 52 and the bearing 53, without enhancing the accuracy of mounting dimensions, detailed detection of rotation states would become impossible because of actuating force decreased due to center misalignment. Another disadvantage is that the eccentricity of the shaft 52 causes wear on the two-point support portions, reducing the operating life of the sensor.